Metal degreasing composition



Patented Aug. 8, 1950 METAL DEGREASING COMPOSITION Arthur W. Lax-char,MendenhallQPag assignor to E. I. du Pont de Nemours &' Company,Wilmington, DeL, a corporation of Delaware No Drawing. Application May13, 1946,- Serial No. 669,459.

This invention relates to'the stabilization of chlorinated hydrocarbonsagainst decomposition and their use as cleaning compositions, such as inthe degreasing of metals. More particularly this invention relates to amethod for preventing or retarding the metal-induced decomposition ofvolatile chlorohydrocarbon solvents and to compositions containingvolatile chlorohydrocarbon solvents stabilized against decomposition,such as is encountered in the degreasing of metals.

Although volatile chlorohydrocarbons are excellent cleaning anddegreasing agents, they possess certain disadvantages when used. incontact with metals. The use of volatile chlorinated hydrocarbons, suchas trichloroethylene', for degreasing metals or in metallic apparatus,has the disadvantage that metals, such as aluminum or iron, tend toinduce and catalyze certain condensation reactions involving thechlorine atoms of the chlorinated hydrocarbons, As a result, the solventmay decompose, sometimes vigorously, with the evolution of products suchas hydrochloric acid or phosgene and the formation of a gummy mass. Thusmetallic apparatus, in which the solvent is used, is subject to severecorrosion and dangerous fumes are given off. It is therefore of greatindustrial importance to prevent or retard. metal-induced decompositionof volatile chlorinated hydrocarbon solvents. Since cleaning treatmentsof metals or other objects are in practice carried out in the vapor aswell as in the liquid phase, it is necessary to prevent decomposition ofthe volatile hydrocarbon solvent in both the vapor and liquid phases.

An object of this invention is to provide a method for preventing orsubstantially retarding the decomposition of volatile chlorinatedhydrocarbon solvents in the presence of metals, such as iron oraluminum. A further object of this invention is to provide a cleaningcomposition comprising a volatile chlorohydrocarbon solvent which isstabilized against metal-induced decomposition. A still further objectis to provide a cleaning composition comprising a stabilized volatilechlorohydrocarbon solvent in which the stabilizer is sufficientlyvolatile to be present in effective amounts in the vapor of thechlorohydrocarbon. Another object is to provide a stabilizer forvolatile chlorohydrocarbons which is effective in low concentration inboth the liquid and vapor phase. An important object is to provide \astabilized chlorinated hydrocarbon solvent for the degreasing of metals.An additional object is to provide a practical and safe method ofdegreasing metals with a volatile chlorohy- 1 Claim. (01. 252-171)carbon solvent.

2 drocarbon solvent. Other objects will appear hereinafter.

These objects are accomplished by adding to the volatile chlorinatedhydrocarbon an effective amount of cyclohexene. It has now beendiscovered that volatile chlorohydrocarbon solvents containingcyclohexene are stabilized toward metal decomposition.

For eiiective results, the cyclohexene should be used in amounts of atleast 0.02 based on the weight of the chlorohydrocarbon. It is ingeneral unnecessary to use more than a small amount, such as 1% ofcyclohexene, a concentration of about 0.05 to 0.25% based on thechlorohydrocarbon being preferred in most instances.

In order to be eiiective in the vapor phase as Well as in the liquidphase, the stabilizer must be volatile with the vapor of the chlorinatedhydro- In practice this requires that the stabilizer should have aboiling point below 175 0., at the most and much preferably below 100 C.for use with the lower boiling chlorohydrocarbons. Cyclohexene, having aboiling point of 833 C. under atmospheric pressure, is not onlyeffective in low concentrations, but is sufliciently volatile to bepresent in efiective amounts in the vapor of the chlorohydrocarbon.

The chlorinated hydrocarbons to which this invention is chieflyapplicable are the volatile chlorohydrocarbon solvents boiling belowabout 150 0., particularly the volatile aliphatic chlorohydrocarbonsolvents, examples of which are chloroform, carbon tetrachloride, andthe lower alkyl chlorides, such as butyl, amyl and hexyl chlorides,dichloroethane, trichloroethylene, tetrachloroethane. However, thisinvention is generally applicable to volatile chlorohydrocarbons andincludes cyclic chlorohydrocarbons, such as chlorobenzene andchlorocyclohexane.

One of the most important of the volatile chlorohydrocarbon solvents istrichloroethylene, and the invention will be further illustrated withreference to this particular solvent. In the following examples, partsare by weight, unless otherwise stated.

Example I In comparative tests, two mixtures of parts oftrichloroethylene and 0.2 part of mesh aluminum powder were held at C.for 24 hours in sealed glass tubes from which substantially all oxygenhad been removed. One sample contained 0.1% by weight of cyclohexene,the other was an unstabilized control. At the end of the test, eachvessel and its contents was washed thoroughly with 100 parts of 5%nitric acid, and the chloride content of the wash liquor was determinedby adding excess 0.02 N silver nitrate solution and back titrating with0.02 N potassium thiocyanate solution, using ferric alum indicator. Itwas found that 100 parts of the unstabilized control contained 0.389part of chloride ion, whereas 100 parts of the sample stabilized withcyclohexene contained only 0.012 part of chloride ion. Thus, in thepresence of cyclohexene, the

extent of trichloroethylene decomposition in this accelerated test wasonly about 3% of what it was in the absence of cyclohexene. Theinhibitory power of cy-clohexene towardmetal-induced decomposition ofchlorohydrocarbons is all the more remarkable when it is compared tothat of such a closely related compound as cyclohexane. Under identicalconditions cyclohexene is seventeen times more effective thancyclohexane.

. Eaiample II The effectiveness of cyclohexene in conjunction with knownoxidation inhibitors for chlorinated hydrocarbon solvents such asaniline, isshown by the following tests. Five hundred and forty (540)parts of trichloroethylene containing 0.04% by weight of aniline wasboiledunder total reflux with 5 parts of 100 mesh aluminum powder and0.5 part of iron powder. Samples were withdrawn periodically and aciditywas determined by titrating with 0.01 N sodium hydroxide. After 13 days,28 cc. were required to neutralize the acid in a 25 cc. sample. In anexactly similar test except that the trichloroethylene contained 0.04%aniline and 0.04% vcyclohexene, a 25 cc. sample taken after 18 daysrequired only 8 cc. of 0.01 N sodium hydroxide. Thus, the presence ofcyclohexene had brought about a more than threefold improvement instabilizing action over aniline alone. When no stabilizer at all is usedin the above-described test, the acidity developed in a 25 cc.samplecorrespondsto 68 cc. of 0.01 N sodium hydroxide after only 24hours refluxing.

If desired, other stabilizers may be used in conjunction withcyclohexene and other beneficial adjuvants, such as known antioxidants,may be added.

The stabilized chlorohydrocarbons made available by this invention findtheir chief use in the cleaning and degreasing of metals or alloys suchas iron, steel, aluminum, nickel, chromiumm, copper, brass, and the likeor of articles made therefrom. However, they are also useful whenever achlorinated solvent is to be used in metallic apparatus as in thetextile cleaning industry or in solvent extraction processes. Thevolatile stabilizer of this invention, cyclohexene, has the furtheradvantage that it can be recovered with the solvent when the latter isdistilled from the oil, grease and dirt left in it after a cleaningoperation, thus avoiding unnecessary waste and economic loss.

As many apparently widely different embodiments of this invention may bemade without departing from the spirit and scope thereof, it is to beunderstood that I do not limit myself to the specific embodimentsthereof except as defined in the appended claim.

I claim: I i

A metal degreasing composition stabilized against aluminum-induceddecomposition in the liquid and vapor phases consisting essentially oftrichloroethylene and from .02% to 25% of cyclohexene based on theweight of said trichloroethylene.

ARTHUR W. LARCHAR.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,949,857 Braun Mar. 6, 19342,371,645 Aitchison et a1 Mar. 20, 1945 OTHER REFERENCES Mellan:Industrial Solvents, Reinhold Pub. Co., N..Y., 1939, pages 154, 156, 179and 181.

